1. Field of the Invention
The invention relates to a hologram recording medium which displays a three-dimensional image by a hologram.
2. Description of the Related Art
A three-dimensional image by a hologram is applied for three-dimensional image recording media for decorative purposes or in the security field of credit cards or ID cards. Of such hologram recording media for image display applications, small-sized hologram recording media have been put into practical use in credit cards or the like; and in recent years, for decorative purposes or advertising purposes or purposes of displaying detailed information in maps or the like, hologram recording media having a larger size are being desired.
Also, in structures of image display media (hologram recording media) by a hologram system, a structure in which a recording layer which is a photosensitive substance is interposed between substrates such as transparent films or glass thin plates is general. As this recording method, there is advocated a method of writing information by refractive index modulation of a major component of the recording layer by a light source with high coherence such as lasers from both planes or one plane of the hologram recording medium (see, for example, Japanese Patent No. 2873126 (Patent Document 1)). According to this Patent Document 1 or the like, two lights having an equal wavelength (namely, object light and reference light) are interfered to generate a wave surface as an interference fringe, and a photoreactive monomer which is a photosensitive material is polymerized and fixed thereon, whereby information is recorded due to a difference in refractive index or transmittivity from other sites. When the original reference light is irradiated thereon, a wave surface the same as in the object light can be reproduced by a diffraction phenomenon.
For the purpose of achieving recording by increasing the screen size of a hologram recording medium, countermeasures such as use of an exposure light source with high intensity and prolongation of an exposure time are general. However, in this method, since the size of device becomes large and a long time is taken, there was involved a problem that the costs increase.